The structure-function properties and signal transduction mechanisms of the AT1 angiotensin II receptor were investigated in adrenal glomerulosa cells and transfected cells expressing wild type and mutant AT1 receptors. Earlier studies identified conserved residues (Tyr215 in the 5th transmembrane domain and an apolar residue, Leu222, in the third cytoplasmic loop) as essential for receptor activation and signal transduction in Ang II-stimulated cells. Further analysis of amino acids in the seventh transmembrane helix revealed that Asn294 is also an important determinant of receptor activation. In addition, the adjacent Asn295 residue is required for normal ligand binding, in particular of non-peptide agonist and antagonist analogs. Specific antisera to native and epitope-tagged AT1 receptors have been utilized to demonstrate agonist-stimulated phosphorylation of the endogenous and transfected receptors. The location and functional significance of such phosphorylation is being analyzed in selected tail-deletion and other mutant AT1 receptors. In addition to signaling through the Gq/phospholipase C pathway in adrenal glomerulosa cell, the AT1 receptor was found to stimulate growth responses through the MAP kinase pathway. This was effected in part through protein kinase C, and also through activation of the ras/raf/mek cascade. The wortmannin-sensitive PI4-kinase previously identified as the enzyme responsible for maintenance of the agonist-sensitive polyphosphoinositide pool in calcium-mobilizing cells was isolated and cloned from bovine adrenal and brain. Two distinct enzymes with the kinetic properties of type-III PI-kinases, with homology with known yeast PI-4-kinases, were identified. The smaller 110 kDa enzyme (PI4KIIIbeta) contains an N-terminal proline- rich region and has homology with the 110kDa catalytic subunit of PI 3-kinases. The larger 210 kDa enzyme (PI4KIIIalpha) shows extensive sequence similarity with a human 97 kDa PI 4-kinase that is probably a splice variant of a larger enzyme that is the human homolog of PI4KIIIalpha. The cloning of these enzymes should facilitate the clarification of their roles in phosphoinositide signaling pathways and regulatory functions in mammalian cells.